Log4j1.x升级Log4j2.x后Tomcat过滤器配置获取值为空求助

问题背景 #

Tomcat 9环境中，web.xml配置了自定义NewSession过滤器，使用Log4j 1.x时运行正常。升级到Log4j 2.17.1后，启动Tomcat出现以下错误，放回log4j-1.2.15.jar可恢复，但必须使用Log4j 2.x版本。

原web.xml过滤器配置 #

<filter>
    <filter-name>newsession</filter-name>
    <display-name>newsession</display-name>
    <description>newsession</description>
    <filter-class>com.demo.custom.filter.NewSession</filter-class>
    <init-param>
        <param-name>DomainName</param-name>
        <param-value>.testlab.com</param-value>
    </init-param>
    <init-param>
        <param-name>DomConfigFile</param-name>
        <param-value>/opt/tomcat/webapp/demoapp/WEB-INF/classes/NAM_log4j.xml</param-value>
    </init-param>
    <init-param>
        <param-name>customPropFile</param-name>
        <param-value>/opt/tomcat/webapp/demoapp/WEB-INF/classes/custom_resources.properties</param-value>
    </init-param>
</filter>
<filter-mapping>
    <filter-name>newsession</filter-name>
    <url-pattern>/idff/sso</url-pattern>
</filter-mapping>

启动错误日志 #

ERROR com.demo.custom.filter.NewSession - No transformation given
ERROR com.demo.custom.filter.NewSession - domConfigFile got null from web.xml, setting hardcoded value
ERROR com.demo.custom.filter.NewSession - custom_resources got null from web.xml, setting hardcoded value
main ERROR Error processing element category ([Configuration: null]): CLASS_NOT_FOUND
main ERROR Unknown object "root" of type org.apache.logging.log4j.core.config.LoggerConfig is ignored: try nesting it inside one of: ["Appenders", "Loggers", "Properties", "Scripts", "CustomLevels"]

过滤器Java代码片段 #

package com.demo.custom.filter;

import javax.servlet.Filter;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.annotation.WebFilter;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletRequestWrapper;
import org.apache.logging.log4j.Logger;
import org.apache.logging.log4j.LogManager;

@WebFilter({ "/NewSession" })
public class NewSession implements Filter {
    static class FilteredRequest extends HttpServletRequestWrapper {
        public FilteredRequest(ServletRequest request) {
            super((HttpServletRequest)request);
        }

        public String getParameter(String paramName) {
            String value = super.getParameter(paramName);
            // 省略业务逻辑
            return value;
        }

        public static String decryptValue(String value){
            String decryptvalue = null;
            // 省略解密逻辑
            return decryptvalue;
        }
    }

    private static String domainName = null;
    private static String domConfigFile=null;
    private static Logger myLogger = LogManager.getLogger(NewSession.class);
    private String custom_resources;

    public void init(FilterConfig fConfig) throws ServletException {
        try{
            domainName = fConfig.getInitParameter("DomainName");
            domConfigFile=fConfig.getInitParameter("DomConfigFile");
            custom_resources=fConfig.getInitParameter("customPropFile");
        }catch(Exception e){
            myLogger.error(e.getMessage());
        }
        if(domainName == null){
            domainName = ".testlab.com";
        }
        if(domConfigFile==null){
            myLogger.error("domConfigFile got null from web.xml, setting hardcoded value");
            domConfigFile = "/opt/tomcat/webapp/demoapp/WEB-INF/classes/NAM_log4j.xml";
        }
        if(custom_resources==null){
            myLogger.error("custom_resources got null from web.xml, setting hardcoded value");
            custom_resources = "/opt/tomcat/webapp/demoapp/WEB-INF/classes/custom_resources.properties";
        }
    }

    // 省略doFilter、destroy方法
}

问题分析 #

1. 过滤器初始化参数失效：过滤器类同时使用@WebFilter注解和web.xml配置，Tomcat中注解配置优先级高于web.xml，而@WebFilter未定义初始化参数，导致fConfig.getInitParameter()无法获取web.xml中配置的值。
2. Log4j配置文件格式不兼容：NAM_log4j.xml是Log4j 1.x的配置格式，其中<category>、直接放置的<root>元素不符合Log4j 2.x的配置规范，导致初始化报错。

解决方案 #

1. 修复过滤器参数获取问题 #

移除过滤器类上的@WebFilter({ "/NewSession" })注解，完全依赖web.xml的过滤器配置，确保初始化参数能被正确读取。修改后的代码片段：

package com.demo.custom.filter;

import javax.servlet.Filter;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletRequestWrapper;
import org.apache.logging.log4j.Logger;
import org.apache.logging.log4j.LogManager;

// 移除@WebFilter注解
public class NewSession implements Filter {
    // 其余代码保持不变
}

2. 迁移Log4j 1.x配置到Log4j 2.x格式 #

将原NAM_log4j.xml转换为Log4j 2.x的XML格式，核心变化：

• 根元素改为<Configuration>，指定Log4j 2.x命名空间
• <category>替换为<Logger>，放置在<Loggers>节点下
• <root>必须嵌套在<Loggers>节点内
• 新增<Appenders>节点管理输出目标

示例转换后的配置：

<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="WARN" xmlns="http://logging.apache.org/log4j/2.0/config">
    <!-- 配置输出目标（Appender） -->
    <Appenders>
        <Console name="Console" target="SYSTEM_OUT">
            <PatternLayout pattern="%d{HH:mm:ss.SSS} [%t] %-5level %logger{36} - %msg%n"/>
        </Console>
        <!-- 可添加File、RollingFile等其他Appender -->
    </Appenders>
    <!-- 配置日志器 -->
    <Loggers>
        <!-- 对应原Log4j1.x的<category> -->
        <Logger name="com.demo" level="info" additivity="false">
            <AppenderRef ref="Console"/>
        </Logger>
        <!-- 根日志器 -->
        <Root level="error">
            <AppenderRef ref="Console"/>
        </Root>
    </Loggers>
</Configuration>

3. 清理依赖确保仅使用Log4j 2.x #

检查项目依赖和Tomcat/lib目录，移除所有Log4j 1.x相关jar包（如log4j-1.2.15.jar），保留以下Log4j 2.x核心依赖：

• log4j-core-2.17.1.jar
• log4j-api-2.17.1.jar
• 若项目使用SLF4J，需添加log4j-slf4j-impl-2.17.1.jar作为桥接包

验证 #

1. 部署修改后的过滤器类
2. 替换NAM_log4j.xml为Log4j 2.x格式配置
3. 清理Tomcat的work目录，重启服务
4. 检查启动日志，确认：
   • 过滤器能正确读取web.xml中的初始化参数，无got null错误
   • Log4j 2.x初始化无CLASS_NOT_FOUND或元素错误

内容的提问来源于stack exchange，提问作者user3441151